Many semiconductor fabrication processes are temperature sensitive and therefore temperature control within process tools is important to producing high yield wafers. Typical temperature control techniques applied in semiconductor fabrication facilities involve providing a separate temperature control system for each tool that needs temperature control. For example, each temperature control system may include its own refrigeration unit, its own heat exchanger, and its own refrigerant distribution system. The one temperature control system-per-tool approach to temperature control has a few drawbacks. One drawback to the one temperature control system-per-tool approach is that each of the individual temperature control systems includes its own, relatively small, refrigeration unit. Smaller refrigeration units are generally less energy efficient and less reliable than larger refrigeration units. Another drawback to the one temperature control system-per-tool approach is that all of the separate temperature control systems take up a large amount of floor space in a fabrication facility. Because the cost per square foot of a semiconductor fabrication facility is extremely high, there is much incentive to minimize the footprint of temperature control systems.
One technique for providing temperature control to multiple process components in a semiconductor processing facility is disclosed in U.S. Pat. No. 6,102,113, issued to Cowans. Cowans discloses a multi-channel temperature control system that is completely contained within a compact mechanical frame. The multi-channel temperature control system utilizes a single refrigeration unit to provide cooling to multiple temperature control channels. Each temperature control channel includes an evaporator/heat exchanger within the compact mechanical frame that utilizes subcooled refrigerant from the common refrigeration unit to cool a heat transfer fluid. The heat transfer fluid is circulated between the evaporator/heat exchanger that is within the mechanical frame and a process tool in order to control the temperature within the tool. Although the temperature control system of Cowans works well to provide multiple temperature control channels within a minimum footprint, the heat transfer fluid that is actually used within the process tool for temperature control must be continuously circulated between the process tool and the evaporator/heat exchanger that is located within the mechanical frame. If the temperature control system is supporting multiple process tools within a fabrication facility, the heat transfer fluid for each tool must be pumped back and forth between the process tool and the tool-specific evaporator/heat exchanger that is located within the mechanical frame. As the distance between the process tools and the multi-channel temperature control system increases, the responsivity of the temperature control system decreases because it takes longer for the heat transfer fluid to travel from the evaporator/heat exchanger to the process tool. Additionally, as the distance between the process tool and the evaporator/heat exchanger increases, the accuracy of temperature control is less reliable because the heat transfer fluid is subjected to different ambient temperature conditions while it is circulated between the process tool and the evaporator/heat exchanger.
Another technique for providing temperature control to multiple process components in a semiconductor processing facility is disclosed in U.S. Pat. No. 6,026,896, issued to Hunter. Hunter discloses a multi-channel temperature control system that includes a common source of heated or chilled fluid that is distributed to multiple remote process tools. Each process tool has a temperature sensor for measuring the temperature of the process tool, a flow control valve for controlling the flow of the heated or chilled fluid to the process tool, and temperature control logic that adjusts fluid flow through the flow control valve in response to temperature measurements from the temperature sensor. Although the temperature control system of Hunter works well to provide individual temperature control for multiple channels from a single source of is heated or chilled fluid, the heated or chilled fluid disclosed in Hunter is used to directly heat or cool the process tools. Because the heated or chilled fluid is used to directly heat or cool the process tools, the range of temperature control possible at all of the process tools is limited by the temperature of the heated or chilled fluid that is circulated through the process tools and the electrical characteristics of the heated or chilled fluid must be compatible with the process tools that are being heated or cooled. In order for the temperature control system to be effective, all of the process tools must have very similar temperature control needs. Additionally, if a process tool requires both a source of heating and a source of cooling, according to Hunter, two parallel fluid supply systems are provided. Although the two parallel fluid supply systems can provide sources of heating and cooling to the same process tool, the parallel supply systems are costly. Additionally, even though the rate of heating or cooling for each process tool can be controlled by controlling the flow rate of the fluid to the tool, the heating or cooling response time is limited by the difference in temperature between the fluid and the actual temperature within the process tool. Although the dynamic range of the temperature control system can be changed by changing the temperature of the circulating fluid, changing the temperature of all of the circulating fluid in the system is a relatively slow process that limits the response time of the system.
In view of the above-identified problems with prior art temperature control systems, what is needed is a temperature control system that is accurate, responsive, energy efficient, and that has a relatively small footprint.